Sauté the onion on a low heat until soft, add the garlic and cook out for a further 5 minutesAdd the grated gingerIn a sauce pan toast the coriander, mustard, cumin and pepper on a medium heat for about 5 minutesPlace the spice mix in a mortar and pestle and adding the salt, grind to a relatively fine powderAdd the spice mix to the pan with the onions and ginger and cook for 5 minsAdd the tomatoes, vinegar, purée and sugar and stir wellBring to the boil for 10 mins stirring constantlyLower to a medium heat and cook for a further 30 minutes allowing the mixture to reduce keep stirring to ensure the chutney does not stick to the bottom of the pan and burnIf it is still not thick enough continue to cook till it reaches a jam like consistencyPour into sterilised jars and place the lids on quicklyAfter one month the chutney is ready to useIt goes really well with strong hard cheeses